A ZnSe single crystal is expected to be used, for example, as a blue light emitting diode. However, conventional ZnSe single crystals are neither large nor of high quality to be used as such diode. A ZnSe single crystal prepared by chemical vapor deposition tends to have crystal defects such as the formation of twin crystals and are not large enough. A ZnSe single crystal prepared by the Bridgman method also tends to have crystal defects such as bubbles, twin crystals and compositional deviations.
In order to grow an epitaxial layer of ZnSe on a substrate, a single crystal of a different material having a similar lattice constant such as GaAs, GaP and Ge is used as the substrate, but an epitaxial layer possessing high qualities cannot be prepared due to the difference between the lattice constants of the ZnSe and the substrate.